Blood tubes for the medical industry have traditionally been prepared from glass. In recent years, the possibility of infectious disease being spread by contact with blood from broken tubes has caused the medical industry to increasingly depend on plastic tubes. Tubes are now being prepared from injection molded resins such as PET. These tubes are prepared and maintained under reduced pressure to allow for a convenient method for the sampling of blood. Because of the need to maintain reduced pressure in these tubes, there is a need for resins that will provide improved barrier properties relative to PET and therefore, give the extended shelf-life needed in selected applications.
Poly(ethylene-2,6-naphthalenedicarboxylate) (PEN) displays improved barrier properties relative to PET. However, this resin is quite expensive and due to the increased melting point and melt viscosity requires very high processing temperatures relative to PET.
U.S. Pat. No. 4,401,805 describes PET copolyesters containing 1-45 mol % of aliphatic dicarboxylic acids containing 3 to 8 carbon atoms which are reported to have good barrier properties. However, the addition of only aliphatic dicarboxylic acids lowers the heat resistance properties of the resultant polyester relative to those of PET. The addition of aromatic dicarboxylic acids other than terephthalic acid is not disclosed.
Research Disclosure No. 36009 (April, 1994) describes PET copolyesters containing either 10-50 mol % isophthalic acid, or 10-30 mol % of either succinic acid, glutaric acid, adipic acid, or mixtures of these aliphatic acids. These copolyesters are reported to be useful for the preparation of blood tubes.
Research Disclosure No. 36903 (January, 1995) discloses PET copolyesters containing glutarate, succinate, adipate or mixutures thereof that are reported to have improved shelf-life in blood tubes. Terpolymers of PET, isophthalic and naphthalenedicarboxylic acids are also disclosed.
Research Disclosure No. 29484 (October, 1988) discloses various PEN copolyesters.